A new update for Apple’s iOS operating system for mobile devices is closing a security hole that made jailbreaking the devices easy for some hackers.

The exploit was part of iOS’s PDF software, which had a security hole in the way iOS handled PDF fonts, according to a Mashable story. That issue could have allowed malware to be inserted into iOS devices when they viewed certain PDFs, and it also allowed hackers to run jailbreaks on the platform.

Root hacking a device, also known as “jailbreaking,” is a process that removes the controls and safeguards installed on a phone by Apple (AAPL). It allows users to change mobile carriers, access alternative app stores and run software on iOS devices that Apple never intended. Apple actively tries to bar users from jailbreaking devices with fresh software updates, but there’s also a pretty robust community on the Internet that is always looking for ways around Apple’s new security upgrades.

Taking away a get out of jail free card for hackers

The PDF exploit made it easy for hackers to get jailbreak the last version of iOS, version 4.3, by running the web-based JailbreakMe 3.0. The new update is supposed to fill that hole, and it does close of the access that malicious hackers might have to iPhones. But as PC World pointed out, it hasn’t stopped jailbreaking of iOS in its tracks – in fact, it took less than 12 hours for a new jailbreak from RedmondPie to appear online and allow users to break down Apple’s defenses yet again.

Unfortunately for the hacking community, RedmondPie’s jailbreak doesn’t work on the iPad 2, which the PDF exploit was able to jailbreak. That ability might come a bit later, allowing iPad 2 owners the same kind of capabilities that iPhone owners often enjoy.

Security risks for jailbroken phones

Although jailbreaking might sound like a good way to shrug off Apple’s sometimes-oppressive iOS controls, it isn’t without its risks. A jailbroken phone is open to a lot more security risks than phones running Apple’s standard iOS programs, which is part of the reason for Apple’s controls in the first place. Downloading apps that aren’t available through the iTunes App Store is nice, but there’s a reason apps take so long to get approved by Apple: the company tries pretty hard to screen out malware and other hidden risks.

Still, if you’re up for the risk, check out RedmondPie’s site, or just sit tight – a new jailbreak is bound to come along before too long. They always do.